Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details) - USD ($) $ in Millions	Jan. 01, 2019	Sep. 30, 2019
Summary of Significant Accounting Policies [Line Items]
Operating lease right-of-use asset		$ 267
Operating lease liability		$ 284
Accounting Standards Update 2016-02 [Member] | New Accounting Pronouncement Effect [Member]
Summary of Significant Accounting Policies [Line Items]
Operating lease right-of-use asset	$ 213
Operating lease liability	213
Operating lease, impairment loss on right of use asset	8
Below market lease intangibles	(25)
Deferred rent liabilities	$ (8)
Maximum [Member]
Summary of Significant Accounting Policies [Line Items]
Operating lease initial term	12 months